Abstract 12594: GRK2 is a Novel Regulator of Cardiac Mitochondrial Bioenergetics

Abstract

Introduction: The GPCR kinase GRK2 is highly expressed the heart; during cardiac injury or heart failure (HF) levels and activity of GRK2 increase. While GRKs are canonically studied upstream of β-adrenergic desensitization, GRK2 has a large non-GPCR interactome and novel, noncanonical functions. We have discovered that in the heart, GRK2 translocates to mitochondria ( mtGRK2 ) following injury and negatively affects cellular metabolism and substrate utilization. Thus, we have sought to identify the mechanism(s) by which GRK2 regulates mitochondrial function. Hypothesis: mtGRK2 phosphorylates proteins involved in mitochondrial bioenergetics, which may explain the altered metabolic phenotype seen following cardiac injury or HF. Methods: Stress-induced mitochondrial translocation of GRK2 was validated in rat ventricular myocytes, murine cardiac tissue and a cardiac-derived cell line. The mtGRK2 interactome was then via protein immunoprecipitation followed by liquid chromatography-mass spectroscopy (LCMS) analysis. Proteomics analysis identified mtGRK2 interacting proteins which were involved in mitochondrial dysfunction. Results: Complexes I, II, IV and V of the electron transport chain (ETC) were identified as mtGRK2 interacting partners. Several mtGRK2 interactions were increased following stress, particularly those with Complex V. We further established that mtGRK2 phosphorylates some of the subunits of Complex V, particularly the ATP synthase barrel which is critical for ATP production. Specific amino acid residues on these subunits have been identified using PTM-LCMS and are currently being validated in a murine myocardial infarction model. Additionally, alterations in either the levels or activity of GRK2 appear to alter the enzymatic activity of Complex V in vitro , thus regulating ATP production in cardiomyocytes. Conclusions: The phosphorylation of the ATP synthesis machinery by mtGRK2 may be regulating some of the phenotypic effects of injured or failing hearts such as reduced substrate utilization. Research is ongoing to further elucidate the novel role of mtGRK2 in regulating bioenergetics and cell death, uncovering a novel, treatable target for rescuing cardiac function in patients with injured or failing hearts.